In the International Patent Application for “Aerial Observation System”, published as WO/2010/032251, there is described a new lighter-than-air platform, which can carry a payload useful for such tasks as aerial surveillance, target designation, target pointing, laser range finding, wireless relaying, and the like. The system differs in its flight characteristic properties from prior art lighter-than-air systems in that it comprises a novel combination of a separated support balloon and a kite, with the payload on the kite, and the balloon supplying buoyancy to the kite by means of a line attached between the balloon and the kite below it. The use of separate kite and balloon modules provides a level of mechanical isolation of the payload on the kite from the effects of buffeting of the balloon in the wind. This isolation effect can be increased by use of longer connecting cords, or by use of one or more flexible sections in the connecting cord or cords, such as a spring, or an elastomeric section. However even with such means, the payload is still subject to the effect of winds and needs to be stabilized either passively or actively.
Passive stabilization has usually been supplied either:
(i) by use of the well known Picavet suspension system, or an adaption thereof, or any other known passive mechanical stabilization system, or
(ii) by use of a suspension system, as described in the above referenced WO/2010/032251, based on the mounting of the payload on the kite by means of a gimbal system, preferably using two generally orthogonal gimbals, thus allowing freedom of roll and pitch motion of the payload relative to the kite. It is to be understood that the terms roll and pitch are used in their normal nautical or aeronautical sense—roll being rotation about an axis generally in the direction of the length of the motion platform, and pitch being rotation about an axis generally horizontally perpendicular to the direction of the length of the motion platform.However, such attempts at stabilization using a plurality of connecting cords or supporting gimbals have had only a limited level of success. In particular, support of the payload by a number of cords may even complicate the motion of the platform as the various suspension points complete with each other in providing reaction to the effect of wind buffeting, or in particular, to the actuation of motors on the payload itself. One particular suspension cord or pair of cords may react in one direction to activation of a motor while another one may try to act in the opposite direction, leading to instability of the platform. Therefore, attempts to use passive stabilization with complex compensating harnesses do not generally provide adequate stabilization in wind conditions.
Active stabilization, as described in the prior art, can be achieved by any of the known methods acting directly on the kited platform connected between the buoyancy balloon and the ground anchor line, such as by the use of angular accelerometer stabilization, or by using GPS referencing to stabilize the platform.
However, such active methods may be expensive and complex to implement, and the passive stabilization methods mentioned hereinabove may not provide sufficient stabilization for a payload which requires accurate stabilization during potentially buffeting winds. Furthermore, the payload may be suspended directly from the balloon without the stabilization advantages provided by the kite. In such instances, a more direct form of stabilization is required in order to take the place of the stabilization effect otherwise provided by the kite. There is therefore need for a simpler and more effective system for providing active stabilization to a balloon borne aerial platform.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.